1. Field
Example embodiments relate to nonvolatile memory devices using resistive elements and a method of manufacturing a nonvolatile memory device.
2. Description of the Related Art
PRAM (Phase change Random Access Memory), RRAM (Resistive RAM) and/or MRAM (Magnetic RAM) are types of nonvolatile memory devices using resistance materials. The DRAM (Dynamic RAM) or a flash memory device stores data by using charges. The nonvolatile memory devices using resistance materials store data by using the change of the state of a phase change material, e.g., a chalcogenide alloy (PRAM), the change of the resistance of variable resistance materials (RRAM), or the change of the resistance of a thin MTJ (Magnetic Tunnel Junction) film depending on the magnetization state of a ferromagnetic material (MRAM).
An example of a PRAM will be described in detail. The phase change material may have a lower resistance in a crystal state and may have a higher resistance in an amorphous state. Accordingly, the crystal state is defined as “set” or 0 data, and the amorphous state is defined as “reset” or 1 data. Further, the PRAM may provide write pulses, e.g., set pulses and reset pulses, to the phase change material, so that the PRAM may perform writing by using joule heat generated due to the pulses. Specifically, when 1 data is written, the phase change material may be heated over a melting temperature by the reset pulses and then quickly cooled to be in an amorphous state. When 0 data is written, the phase change material may be heated in the range of a crystallization temperature to a melting temperature and maintained at that temperature for a predetermined or given time. The phase change material may be cooled to a crystal state.
Increased integration of the PRAM is important for joule heat generated during the writing of data in specific phase change memory cells to have an effect on adjacent phase change memory cells. Specifically, even though specific phase change memory cells are cooled during the writing of 1 data, the temperature in the vicinity of the specific phase change memory cells may be relatively high. As a result, data may be written in undesired phase change memory cells.